Komakuk Polygon

The active layer core from the centre of Komakuk Polygon (YC12-KP-Mc) had a median basal age of 1597 cal. yrs BP (Table 5.1). The core showed a distinct sedimentary facies break at 14 cm depth. CONISS ordination validated by broken stick modelling supported two zones KP_c1 and KP_c2 for the core, which corresponded with the facies break and were mainly distinguished by a sharp increase in TOC (Figure 5.3a).

In zone KPc1 (14-33 cm depth), TOC ranged from 7.5 wt.% to 17.1 wt.% (mean: 9.5 wt.% ± 2.0), and TOC/TN showed low values between 15.3 and 20.4 and a small standard deviation (mean: 17.5 ± 1.3). Stable carbon isotopes δ¹³C had their highest values in this zone, ranging from -28.8‰ to -26.3‰ (mean: -28.1‰ ± 0.6). In KPc1, inorganic material was fine-grained, consisting of clayey silt and sandy silt, with about 20 percent plant material. A mixture of mesic terrestrial (wood fragments, occasional remains of Betula glandulosa, Ledum decumbens, cf. Ranunculus lapponicus), wet terrestrial (occasional Carex sp. seeds) and aquatic (Menyanthes trifoliata, Potamogeton sp.) plant macrofossils was preserved in this zone (Table 5.2).

Zone KPc2 (0-13 cm depth) uniformly showed very high TOC contents between 37.9 wt.%

and 44.2 wt.% (mean: 41.4 wt.% ± 2.2). TOC/TN increased towards the top of the core, ranging between 14.3 and 33.1 (mean: 21.2 ± 6.0), while δ¹³C decreased slightly, ranging from -30.2‰ to -28.0‰ (mean: -28.7‰ ± 0.7). The grain size composition was classified as silty sand. The amount of plant material rose to 100 percent in this zone (Table 5.2). Mesic (Betula glandulosa, Ledum decumbens, Eriophorum vaginatum) and wet taxa (Carex sp.) were found, and remains of aquatic plant taxa were absent. The active layer core from the rim of Komakuk Polygon (YC12-KP-Mr) showed a hiatus of about 5000 cal. years between 16 cm and 17 cm depth (Table 5.1). The identified seeds and leaves of terrestrial plants from the upper part of the core (0-16 cm) showed ages within the last 300 years, while samples below that depth were dated to the middle Holocene (median ages: 5507 cal. yrs BP in 17 cm depth, 5798 cal. yrs BP in 24 cm depth, 4641 cal. yrs BP in 31 cm depth), with an age inversion at the base of the core. A sedimentary facies break was evident at 14-15 cm depth, and two stratigraphic zones were delineated on the basis of CONISS ordination and broken stick modelling. In the upper zone, two subzones were identified. The boundary between zones KP_r1 and KP_r2 corresponded roughly with the age hiatus.

Table 5.1. Results of Accelerator Mass Spectrometry (AMS) radiocarbon dating.

COL2652.1.1 8-9 107 ± 33 31-257 115 Betula glandulosa twig and leaf, Eriophorum vaginatum seed, Cyperaceae leaf

Poz#2-56521 15-16 -464 ± 37 NA NA Ledum decumbens leaf

COL2653.1.1 16-17 4749 ± 40 5336-5583 5507 Dwarf shrub twig and bark, Carex seed, Cyperaceae leaf

COL2654.1.1 23-24 5031 ±41 5718-5890 5798 Carex seed, Cyperaceae leaf, wood Poz#2-56522 30-31.5 4110 ± 73 4525-4811 4641 Carex seed, dwarf shrub leaf YC12-KP-Mc (active layer core from polygon centre)

Poz#2-56519 30-31 1697 ± 25 1559-1681 1597 Betula glandulosa catkin scale, Ledum decumbens leaf,

Carex seed, Menyanthes trifoliata seed Roland Polygon

YC12-RP-Mr (active layer core from polygon rim)

COL2655.1.1 8-9 42 ± 32 NA NA Betula glandulosa leaf and fruit, Ledum decumbens leaf

COL2656.1.1 11-12 124 ±33 21-267 125 Betula glandulosa leaf and twig, dwarf shrub twig Poz#2-56550 13-14 -336 ± 24 NA NA Betula glandulosa leaf, Ericaceae leaf

COL2657.1.1 16-17 4426 ± 58 4877-5261 5035 Betula glandulosa twig, Carex seed, Cyperaceae leaf COL2658.1.1 18-19 5871 ± 59 6634-6779 6691 Carex seed, Cyperaceae leaf

Poz#2-56551 26-27 6192 ± 34 7021-7163 7085 Ericaceae leaf, Carex seed YC12-RP-Mc (active layer core from polygon centre)

COL2659.1.1 11-12 170 ± 36 0-284 176 Betula glandulosa leaf and fruit, Ledum decumbens leaf

Poz#2-56547 13-14 177 ± 40 0-286 176 Ledum decumbens leaf

COL2660.1.1 13-14 185 ± 33 0-285 180 Betula glandulosa leaf and fruit, Ledum decumbens leaf, Carex seed

COL2661.1.1 20-21 592 ± 33 547-639 603 Betula glandulosa twigs, Ledum decumbens leaf, Carex seed, wood

Poz#2-56549 25-26 6147 ± 37 6982-7156 7058 Ericaceae leaf remains Ptarmigan Polygon

YC13-PP-Mr (active layer core from polygon rim)

COL2651.1.1 13-15 1199 ± 55 1058-1228 1127 Cyperaceae leaf remains PG2161 (permafrost core from polygon centre)

COL2650.1.1 83-88 5609 ± 42 6318-6432 6380 Terrestrial plant remains

Figure 5.3. Stratigraphic diagrams showing sediment parameters and established zonation (a) in the centre core and (b) in the rim core of Komakuk Polygon. Parameters used in the CONISS analysis are shown in black, while additional parameters not used in this analysis are shown in grey. The age ranges shown are calibrated 1 sigma ranges based on AMS radiocarbon dates (Table 5.1). The presence of aquatic organisms in the macrofossil record is indicated by hatching.

In zone KPr1 (16-31 cm depth) TOC values exhibited strong variability between 17.9 wt.%

and 40.4 wt.% (mean: 26.8 wt.% ± 6.7) without a clear trend, and stable TOC/TN values between 18.3 and 29.5 (mean: 24.1 ± 2.9). A narrow range from 27.8‰ to 29.0‰ (mean: -28.3‰ ± 0.4) was observed in δ¹³C values, with a slight decreasing trend. Grain size composition fluctuated between sandy silt and silty sand in KPr1 (Figure 5.6). Wood fragments and identifiable plant macrofossils were abundant in the zone, especially in the lower part, where seeds of the wet terrestrial Carex sp. dominated, accompanied by

occasional seeds of the aquatic Potamogeton sp. and Potentilla palustris as well as remains of mesic terrestrial Betula glandulosa and Ledum decumbens (Table 5.2).

Table 5.2. Summary of identified vascular plant macrofossils from the centre and rim cores of Komakuk Polygon. The overall composition of the sieving residue is described by giving the amount of plant material after sieving through 1 mm mesh size and the respective estimated amounts of Bryophyte, Cyperaceae and wood remains in each sample. Plant macrofossils that have been picked and further identified are ordered by hydrological requirements from taxa found under mesic conditions typical for ice-wedge polygon rims to taxa found in wet conditions typical for ice-wedge polygon centres. Finally, aquatic plant remains typical for subarctic ponds and lakes are listed.

Depth (cm) median age (cal yrs BP) amount plant material in sample (ml) amount Bryophytes in sample (ml) amount Cyperaceae in sample (ml) amount wood in sample (ml) Betula glandulosatwig Betula glandulosaleaf (fragment) Betula glandulosafruit Betula glandulosacatkin scale Ledum decumbensleaf Vaccinium vitis-idaea leaf Eriophorum vaginatum seed cf.Ranunculus lapponicusseed dwarf shrub twig fragment dwarf shrub leaf fragment Carexsp. seed Menyanthes trifoliata seed Potentilla palustris seed Potamogetonsp. seed

Zone

Terrestrial ^Aquatic

_{mesic general wet emergent} ^sub-

merged Komakuk Polygon centre core YC12-KP-Mc (active layer)

10 50 12.5 37.5 <0.1 1 1 1+ 3 3 KPc2

14 20 0 14 6 2 2

15 10 0 2 8 1 ^{4 KPc1}

16 10 0 2 8 ^{1 1 3}

31 1597 7 0 2.1 4.9 1 1 1 1 1

32 10 0 4 6 1 1 1

33 10 0 4 6 ^{1 2 1}

Komakuk Polygon rim core YC12-KP-Mr (active layer)

5 50 30 7.5 12.5 5 4+ 1 14+ 18+ 20 1 KPr2B

9 115 50 7.5 27.5 15 52 5 1 2 1+ 2 +++ 3 KPr2A

14 50 0 40 10 ^{2 1}

15 50 0 47.5 2.5 ²

16 modern 25 0 20 5 ^{1 KPr1}

17 5507 35 0 31.5 3.5 ^{1 6 2 1}

23 50 0 45 5 ¹²

24 5798 45 0 27 18 ^{1 14 1}

29 45 0 31.5 13.5 3 43 1

31 4641 40 0 32 8 4 1 4 2 23 2

Zone KP_r2 (0-15 cm depth) showed very high and uniform TOC contents between 35.7 wt.%

and 42.5 wt.% (mean: 40.2 wt.% ± 2.1). TOC/TN ratios lay between 18.1 and 63.7 (mean:

36.9 ± 15.6) and increased strongly towards the top of the core, and δ¹³C values ranged from -29.2‰ to -27.4‰ (mean: -28.2‰ ± 0.5). The two subzones were distinguished by an increase in TOC/TN from zone KP_r2A (7-15 cm depth, mean: 25.8 ± 6.6) to zone KP_r2B (0-6 cm depth, mean: 53.5 ± 7.3). Grain size analyses classified inorganic particles in KPr2A as silty sand and sandy silt. Very little inorganic material was present in KPr2B, and grain size analyses could not be carried out. Mesic terrestrial taxa (Betula glandulosa, Ledum decumbens, Vaccinium vitis-idaea, Eriophorum vaginatum) dominated in this zone, while remains of wet terrestrial taxa (Carex sp.) were scarce and aquatic taxa (Potamogeton sp.) disappeared above 15 cm core depth (Table 5.2). There was a strong increase in remains of mesic terrestrial taxa from KP_r2A to KP_r2B.